Given the prevalence of overweight and obesity, worksite-based health promotion programs have been recommended due to their potential reach and social support impact. Within worksite contexts, many strategies to prevent and treat obesity have focused on educational programs delivered in person or to small groups that target knowledge acquisition, and strategies targeted at individuals to improve dietary and activity practices. These programs have been criticized because they typically reach a small percentage of workers-and seldom those that could benefit most, are of short duration, and have small, temporary effects. They have also typically been conducted in large worksites that have the greatest resources. The lack of success of these programs may be due to: 1) inadequate intervention intensity, 2) implementation challenges, and 3) a lack of theoretical models as the bases for intervention development. To overcome the limitations of previous research we will conduct a 3 group RCT to determine the reach and effectiveness of an extensive intervention that: a) is based upon sound theory, b) is delivered primarily through scalable interactive technologies, and c) leverages the organizational and environmental context of the workplace. We will test the utility of a social ecological theory, individually-targeted internet-based intervention with monetary incentives to reduce the weight of overweight and obese employees (INCENT) when compared to a health risk appraisal and stress management control (HRA). Participants in INCENT will receive frequent e-mail supports that facilitate goal setting, regular assessments of body weight, and incentives based on percent of original body weight lost at the end of each quarter over the 12-month program. The e-mail supports will target improving perceptions of self-efficacy and outcome expectations related to weight loss or maintaining a healthy weight in addition e-mail support will facilitate participant problem solving and identification of resources for healthful eating and physical activity at home, in their neighborhoods, and at their worksite. Given the well-documented rate of recidivism following weight loss programs, a secondary study aim, is to determine the effectiveness of a weight maintenance intervention delivered after the original 12-months of intervention. The weight maintenance intervention will target regular physical activity, healthful food choices, and identification of local resources to support maintaining a healthful weight. It will be delivered via automated interactive voice response (IVR) telephone counseling, based on social ecological theory and support weight loss (i.e., for those who are not yet <BMI of 25) or weight maintenance (i.e., for those with a BMI <=25). In a 3 group worksite cluster randomized design, 48 small to medium sized worksites, with a heterogeneous ethnic (i.e., >20 percent Latino) and economic diversity will be randomized to receive HRA (n=1Q worksites), INCENT (n=19 worksites), or INCENT+IVR (n=19 worksites).